Unlike inorganic semiconductor light emitting devices, polymer light emitting devices are generally simple and relatively easy and inexpensive to fabricate. Also, a variety of colors and large-area devices are easily attained. However, one major problem in prior art polymers used in light emitting devices is that most of them have relative low quantum efficiency. For example. poly(phenylene vinylene) (PPV), one of the most studied polymers for LED application, has electroluminescence (EL) quantum efficiency approximately 0.06% with magnesium as metal electrode. Therefore the challenge is to improve the fluorescent efficiencies of polymers so that polymer light emitting devices can be practically useful.
Previous work on organic light emitting devices has shown that the EL quantum efficiency of a dye-doped small molecular organic thin film is about 3-4 times higher than that of an undoped film. In the prior art of polymer light emitting devices, some improvement in quantum efficiency is also achieved by dispersing fluorescent dye molecules into polymer matrix, but the resulting devices are normally not stable due to either aggregation or crystallization of the doped dyes from the polymer matrix. In the case of PPV, there has been no successful prior art in dye-doping because of its close packed rigid crystalline backbone.
It is a purpose of the present invention to provide a conjugated polymer for use in light emitting devices with improved efficiency.
It is another purpose of the present invention to provide a polymer for use in light emitting devices which has stable and uniformly distributed dye molecules which are chemically bonded to the polymer and uniformly fluorescent.
It is a further purpose of the present invention to provide a polymer for use in light emitting devices which is relatively easy and inexpensive to manufacture.
It is still another purpose of the present invention to provide specific methods to incorporate dye molecules as fluorescent centers into a conjugated polymer.